Conventional bicycle frames use metal tubes welded into closed frameworks to interconnect the components (front fork/handlebar assembly, seat, crankset, rear wheel) and transmit the loads therebetween. The metal tubes keep the components in spacial relation, i.e., they maintain the components relative proximity. Moreover, the metal tubes bear the in-plane and out-of-plane loads between the components.
The traditional bicycle frame comprises: a top tube connected at its front end to the top of the relatively short head tube, and extending generally horizontally backward to the top of the seat tube; a down tube connected at the front end to the bottom of the head tube and extending downwardly and rearwardly to the bottom bracket where the seat tube and the down tube are connected; and pairs of chain stays and rear wheel stays extending backward to dropouts which support the rear wheel axle. This conventional frame design is called the "diamond" frame, because when viewed from the side, the top tube, down tube, chain stays, and rear wheel stays enclose a diamond-shaped space.
Such frames require that the entire frame be re-designed for the different size frames required to accommodate riders of different heights. This includes determining the tube lengths needed for the proper spacing of the bicycle component, cutting the tubes accordingly, determining the tube joint angles, and accordingly welding or brazing the tubes together. This method is time consuming and costly, both in terms of design and manufacturing complexity. Therefore, it is desired to have a frame that is easier to manufacture, particularly when manufacturing different frame sizes.
Furthermore, conventional tube frames are relatively heavy, since they are formed from the extrusion or rolling and seaming of metal alloys. Finally, conventional tube frames are limited in terms of aerodynamic improvements, as they are restricted to the use of tubes of generally circular cross-sections.
It is known to manufacture bicycle frames entirely from composite materials such as in U.S. Pat. No. 4,889,355 to Trimble, wherein the frame is constructed using an internal pressure mold to form composite tubes. However, this manufacturing method does not take advantage of the use of different materials or appropriate configuration to bear the different loads to which a bicycle frame is subject to in use.
Another example of a frame known in the art is seen in U.S. Pat. No. 5,456,481 to Allsop, et al., which discloses a frame having right and left body units which mate directly to each other. All structural elements of the frame are formed from the same material. Again, this manufacturing method does not take advantage of the use of different materials or appropriate configuration to bear the different loads to which a bicycle frame is subject to in use. Therefore, there is a need for a bicycle frame having separate structural elements manufactured such that the various elements take advantage of the different properties of the materials or configurations, thus permitting the most efficient possible frame for all expected loads.
In the conventional bicycle frame design, the seat support is designed integral to the seat tube: the top of the seat tube is notched, and the notch is provided with a screw clamp. The inner diameter of the seat tube is selected to slideably receive a standard seat post, and the clamp is tightened to secure the seat post in the desired vertical position. This conventional seat support design requires that the seat tube be bored to a very precise diameter so that it will accept the seat post, while at the same time not being so large as to require significant distortion of the seat tube's cross-sectional shape when the screw clamp is tightened. Furthermore, the use of a single screw clamp provides only a single point of support for the seat post. The inside diameter of the seat tube is by necessity larger than the outside diameter of the seat post, therefore there will be play between the seat post and the part of the seat tube below the clamp. In this situation, the single support leaves the seat post free to deflect or vibrate within the seat post tube in response to moments around that point of support. Therefore, it is desired to provide a seat support assembly which does not require precise machining, and which provides more than a single point of positive support for the seat post.
Thus, the need exists for a strong, lightweight bicycle frame which is easy to manufacture, which uses different materials in different parts of the frame to most effectively take advantage of the properties of those materials, which can easily accommodate different size frames using standard components, and having an improved seat support assembly.